• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.29.5-30
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• 2020

We present an improved weak-lensing (WL) study of the high-z (z=0.87) merging galaxy cluster ACT-CL J0102-4915 ("El Gordo"), the most massive system known to date at z > 0.6. El Gordo has been known to be an exceptionally massive and rare cluster for its redshift in the current ΛCDM cosmology. Previous multi-wavelength studies have also found that the cluster might be undergoing a merging event showing two distinctive mass clumps and radio relics. The previous WL study revealed a clear bimodal mass structure and found that the entire system is indeed massive (M200a = (3.13 ± 0.56) × 1015 Msun). This mass estimate, however, was obtained by extrapolation because the previous HST observation did not extend out to the virial radius of the cluster. In this work, we determine a more accurate mass estimate of the cluster using WL analysis utilizing a new set of WFC3/IR and wide-field ACS observations. While confirming the previous bimodal mass structure, we find that the new data yield a ~20% lower mass for the entire system (M200a = (2.37 ± 0.28) × 1015 Msun). We also discuss the rarity of the cluster in the ΛCDM paradigm and suggest an updated merging scenario based on our new measurement.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.41.3-42
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• 2021

Coma cluster (Abell 1656) is one of the most massive local galaxy clusters such as Virgo, Fornax, and Perseus, which holds a large collection of globular clusters. Globular cluster systems (GCSs) in a galaxy cluster tell us a history of hierarchical cluster assembly and intracluster GCs (ICGCs) are known to trace the gravitational potential of the galaxy cluster. Previous studies of GCSs in Coma mainly utilized data obtained using Hubble Space Telescope (HST) with high spatial resolution. However, most of the data were based on narrow-field pointing observations. In this study we present the widest survey of GCSs in the Coma cluster using the archival Subaru/Hyper Suprime-Cam (HSC) g and r images, supplemented with the archival HST images. The Coma GCSs are largely extended in E-W and SW direction, along the general direction of Coma-Abell 1367 filament. This global structure of the GCSs is consistent with the spatial distribution of the intracluster light (ICL). ICGC spatial distribution is largely extended to almost ~50% of the virial radius. Most of these ICGCs are blue and metal-poor, which supports the scenario that ICGCs are mainly originated from dwarf galaxies and some proportion from brighter galaxies. Implications of the results will be discussed.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.38.1-38.1
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• 2008

Tides caused by the Galactic gravitational field affect the current dynamical structure of globular clusters in the Galaxy. Indeed, the observed feature of tidal tails stretching beyond globular clusters' tidal radii provides a key information of interaction with the gravitational field of the Galaxy and kinematical orbit of the clusters, which can be an evidence of the merging scenario of the Galaxy formation and evolution. To find such a tidal feature, we have studied spatial density distribution of stars around five globular clusters in the Galactic halo and one cluster in the Galactic bulge, for which we have used wide-field deep photometric data of gri and JHK bands obtained from the MegaCam and WIRCam of the CFHT. Applying the statistical contrast filtering of field stars in the color-magnitude plane of detected stars around five halo clusters, we have found features of tidal tails for four clusters M53, M15, NGC 5053, and NGC 5466. The detected over-density tidal features are well aligned with the cluster's orbits and stretched into the direction of the Galactic center. Statistical analysis indicate that these tidal tails are believed to be cluster stars that have escaped due to the tidal effects to the clusters. A similar tidal feature to that of halo clusters is also detected for the bulge cluster NGC 6626, while the over-density feature seems to be extended into the Galactic plane rather than into the orbital direction and the Galactic center. Conclusively, our result adds further observational evidence of the merging scenario of the Galaxy formation and evolution.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.33 no.3
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• pp.169-175
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• 2010

Recently, to improve operating efficiency with the higher in-line rate in automated production lines, a lot of cases of grouping machines and material handling system together to form a cluster has shown frequently. This article addresses the job allocation and operation method of automated material handling for cluster-type production systems. First of all, the control problems of the automated material handling systems are classified into the control problem of inter-cluster material handling system and that of intra-cluster material handling system. Then, a distributed agent-based control scheme is proposed for the former, and an operational control procedure for the latter. Simulation experiment shows that the proposed method is efficient in reducing cycle times and improving utilization of material handling vehicles.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.78.1-78.1
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• 2013

The hierarchical model of galaxy formation predicts that galaxy halos contain merger relics in the form of long stellar stream. Thus, tidal substructure of stars around globular clusters, such as tidal tails, could be an essential evidence of the merging scenario in the formation of the Galaxy. From April 2010 to December 2012, we obtained $45^{\prime}{\times}45^{\prime}$ wide-field JHKs near-infrared photometric imaging data for about 20 globular clusters in the Milky Way, and examined the stellar density distribution around globular clusters. Here, we introduce the preliminary results of stellar spatial distributions and radial surface density profiles of four globular clusters. In order to minimize the field star contamination and identify the cluster's member candidates stars, we used a statistical filtering algorithm and gave weights on the CMDs of globular clusters. In two-dimensional stellar density maps, we could found tidal stripping structures for some globular clusters. The orientation of tidal substructure seems to associate with the effects of dynamical interactions with the Galaxy and cluster's orbit. Indeed, the radial surface density profile accurately describes this stripping structures as a break in the slope of profile. The observational results could give us further observational evidence of merging scenario of the formation of the Galaxy.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 2002.05a
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• pp.221-228
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• 2002

The NAVER is based on a cluster of low-cost personal computers. The goal of NAVER is to provide flexible, extensible, scalable and re-configurable framework for the diverse virtual environments especially for Gamsung research experiments. Personal computers are divided into three servers are according to their specific functions: Render Server, Device Server and Control Server. While Device Server contains external modules requiring event-based communication for the integration, Control Server contains external modules requiring synchronous communication every frame. And, the Render Server consists of 5 managers: Scenario Manager, Event Manger, Command Manager, Interaction Manager and Sync Manager. In this paper, we discuss NAVER as effective distributed system and its application to Gamsung experiment.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.71.2-71.2
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• 2016

Merging galaxy clusters, such as PLCKG287.0+32.9, provide a window into the formation process of the large scale structure of the universe. PLCKG287.0+32.9 is an enormous merging galaxy cluster with mass estimated to be ~10^15 Msun. It hosts a pair of mega-parsec sized radio relics with projected offsets from the X-ray center of approximately 350kpc and 2.7Mpc, suggesting a NW-SE merging scenario with relics originating from two separate passes (Bonafede et al. 2014). A detected radio halo coincides with the center of x-ray emission. We present the motivation for our weak lensing study of the merging galaxy cluster PLCKG287.0+32.9 using recent Subaru optical imaging. We discuss the basics of weak-lensing and the criteria for source selection. In addition, we describe our method of PSF modeling and mass reconstruction.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.33.3-34
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• 2018

Galaxy clusters contain a diffuse component of stars outside galaxies, that is observed as intracluster light (ICL). Since the ICL abundance increases during various dynamical exchanges of galaxies, the amount of ICL can act as a measurement tool for the dynamical stage of galaxy clusters. There are two prominent ICL formation scenarios; one is related to the brightest cluster galaxy (BCG) major mergers, and the other to the tidal stripping of galaxies. However, it is still under debate as to which is the main ICL formation mechanism. In this study we improve on earlier observational constraints of the ICL origin, by investigating it in a massive fossil cluster at z~0.47. Fossil clusters are believed to be dynamically matured galaxy clusters which have dominant BCGs. Recent simulation studies imply that, BCGs have assembled 85~90% of their mass by z~0.4 (e.g., Contini et al. 2014). Thus our target is an optimal test bed to examine the BCG-related scenario. Our deep images and Multi-Object Spectroscopic observations of the target fossil cluster (Gemini North 2018A) allow us to extract the ICL distribution, ICL color map and ICL fraction to cluster light. We will present a possible constraint of the ICL origin and discuss its connection to the BCG and the host galaxy cluster.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.40.1-40.1
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• 2019

We utilize times since infall of cluster galaxies obtained from Yonsei Zoom-in Cluster Simulation (YZiCS), the cosmological hydrodynamic N-body simulations, and star formation rates from the SDSS data release 10 to study how quickly late-type galaxies are quenched in the cluster environments. In particular, we confirm that the distributions of both simulated and observed galaxies in phase-space diagrams are comparable and that each location of phase-space can provide the information of times since infall and star formation rates of cluster galaxies. Then, by limiting the location of phase-space of simulated and observed galaxies, we associate their star formation rates at z ~ 0.08 with times since infall using an abundance matching technique that employs the 10 quantiles of each probability distribution. Using a flexible quenching model covering different quenching scenarios, we find the star formation history of satellite galaxies that best reproduces the obtained relationship between time since infall and star formation rate at z ~ 0.08. Based on the derived star formation history, we constrain the quenching timescale (2 - 7 Gyr) with a clear stellar mass trend and confirm that the refined model is consistent with the "delayed-then-rapid" quenching scenario: the constant delayed phase as ~ 2.3 Gyr and the quenching efficiencies (i.e., e-folding timescale) outside and inside clusters as ~ 2 - 4 Gyr (${\propto}M_*^{-1}$) and 0.5 - 1.5 Gyr (${\propto}M_*^{-2}$), Finally, we suggest: (i) ram-pressure is the main driver of quenching of satellite galaxies for the local Universe, (ii) the quenching trend on stellar mass at z > 0.5 indicates other quenching mechanisms as the main driver.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.58.2-58.2
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• 2018

Fossil groups of galaxies have characteristic features of a dominant central elliptical galaxy (${\Delta}M_{12}$ > 2 in $0.5R_{vir}$) embedded in highly relaxed X-ray halo, which indicates dynamically stable and evolved systems. These are thought as a final stage of the evolution of galaxy groups in the hierarchical structure formation scenario. However, the formation and evolution of fossil clusters are still unclear due to lack of detailed studies. Therefore, we perform a kinematic research of a known fossil cluster Abell 2261 (A2261 hereafter) using spectroscopic data of 589 galaxies in the A2261 field. Even though A2261 is known as a fossil cluster, previous studies found several unusual features such as quite high X-ray entropy for a stable cluster, and an elongated shape, which are not expected in standard fossil clusters. Using the caustic method, we identify cluster member galaxies and discover a second bright galaxy (${\Delta}M_{12}=1.68$) at ${\sim}1.5R_{vir}$. The presence of such a bright galaxy can break the current fossil state of cluster in the near future. In addition, with two independent substructure finding methods, we confirm that the previously detected elongated galaxy distribution of the cluster is a real feature. These findings indicate that A2261 is not in a fully stable state, unlike the existing fossil definition diagnostic. We require a more stringent criterion for the fossil definition to represent a genuinely final stage of cluster evolution.